Glass compositions



Ap 5 'J.JERGER,JR I 2,833,292

- Y GLASS COMPOSITlONS Filed May 23, 1957' INVENTOR JOSEPH JE'IPGEE, J?

United States Patent Corporation ofrAmerlcauNeWHydePark, N-.Y., acorporationtof New York:

Ap licanemm zs; 19s7, seria1.No. 661,057 2.1Claiins.. chaos-41 Thisinvention relates to .glass'es produced from ternary mixtures of theelements arsenic, sulfur and tellurium.

This application. is ;a; continuation-impart of my copending applicationU.Sl Seri'alINo. 466,737, filed Novembert.4,r195.4,;now abandoned.

In the indieated'fgl'ass field, arsenic trisulfide has been knowntoproduce homogeneous. glass-es. Such glasses have certain transmissionproperties selective to the infrared spectrum but their transmissioncut-ofi does not extend as far into the infraredis often: desirable. Forexample, arsenic. trisulfide .glass will selectively transmit infraredradiation up to. a] wave. length of about 12.5 microns as. measuredacross a .lens. :2 mm. thick at 10% transmission.

Insofar as the present. application is concerned,. infra-. red rays are.dividediinto, .two wavelengthcategories (1) near infrared whiehltincludes.wavelengths. ranging from the endlofltheyisibleflspectrum,.i-.e. about0.,7 micron, up to about 2 or 3 microns,and (2.). far infrared which ranges from about 2.5 up to about 25microns.

In. detectingfievices such as. .infraredspectrometers, gas =analyzers,.,radiation...pyrometers, bolorneters, etc., it isimportantthatflthet opticalfgl'ass employed be selective toinfraredradi'ation It ,is desirable. :that the infrared deviceoperate.selectively and' flexibly over as: wide a wavelength range aspossible, e.g. 215 'to 16' microns, preferably in the range of about, 8.to. 13 microns. in .applications involving I a transmission? path from apoint source of radiation through the atmosphereto an infrared detector.

. In. copendingtf application Ser. No. 372,540. (now abandoned),filedtAugust 5;.19'53, in the name of Walter- A. Fraser, binary mixturesof As S andAs Te havebeen proposed and found to be desirably selectiveto infrared radiation, .provided 1 the: binary: mixtures are rcontrolledover a narrow range of compositions. However, these glasses have certainlimitations in thattheir response to thet8 to. 13 micron range is not ashighas desired:

Ihave found" a more suitable range of glasses of a broader range ofselectivity to the infrared spectrum based on the ternary compositionAs--S--Te. The amounts of elements present in the range do notcorrespond to the binary mixtures of the compounds As S and As Te and;therefore, are not as narrowly limited.

It is accordingly an object of the invention to provide a new field ofglass compositions of the character indicated.

It is another object to provide improved infrared transmitting glasses.

A further object is to provide new glasses meeting the above objects andyet substantially opaque to visible light.

Still another object is to produce an improved infraredtransmittingglass of the character indicated and having a minimum proportion byweight of sulfur.

It is also an object to produce an improved infraredtransmitting glassof the character indicated and having a minimum proportion by weight ofarsenic.

Other objects and various further features of novelty L 't v andinvention will be pointed out or will occur to those skilledin thei artfrom a reading of the following specification, in conjunction with theaccompanyingrtriaxial diagram: Said diagram depicts a-field' of glassesin which the substantial. components are the elemental materialscharacter indicated wasbased on the knowledge that arsenic-trisulfide(AS 8 and certaintmixturest of'arsenic trisulfide with arsenictritelluride (AsgTe y were; of

themselves, glassy anddesirable mixtures of' these com poundscouldbe-produced, butI have discoveredthatde sirable glasses may be.formed in substantial ternary regions not relying;on the use of thesecompounds.

The-compositions provided by the invention are shown by referring. to'the accompanying triaxial diagram in which the 'left-hand cornerrepresents percent arsenic (As), the right-hand corner representsl00.pcrccnt telluriurn (To), and the-upper corner represents. 100percent sulfur (S) Any'point in the diagram representsa definitecomposition; for example, point X represents a-glasscompositionscontaining 40 percent arsenic, 40% sulfur, and 20%tellurium..

The area enclosed by solid line L in. the diagram is.

empirically developed andcovers compositions: provided by the inventionsThus, the solid lineadelineates the.

border: between compositions which will. definitely form.

glasses andthose which become crystalline. Close to this bordenlhavetplotted certain specific compositions which have been made. Thepoints within the area definedby line L are eachtidentified by a smallcircle (0). Good glasses for the purposes of this invention will formfrom compositions anywhere in. this area. Points outsidethe enclosedareaw are designated by a. cross. represent purely crystallinecompositions, and other pointstnear the border are designated byatcrossin a circle (8) and represent generally glassy materials with. somecrystalline content. Examples of good glasses indicated in the areaenclosed by solidilineLare as follows:

Designation Percent: Percent Percent As S Te 55 40 5 50 35 15 40 40 2045 so 25. 20 40 40 20; 35 45-. 15 40 45 15 t 60 i 25' The diagram showsthat compositions along the binary baseline between arsenic and sulfurare glassy, as long as the percentage by weight of arsenic is less thansubstantially 62% and more than 13%; this is in accordance with thedisclosure in my copending patent application Ser. No. 417,724, fi'ledMarch 22, 1954. However, glasses formed by the binary AsS are limited asto cut-off wave length. The transmission properties are improved by theaddition of tellurium and makes available a whole new group ofcompositions characterized by an improved combination of opticalproperties. If tellurium is added to replace part of the sulfur, theproportion by weight of sulfur can be reduced to as low a figure asabout 25 Without devitrification of the melt. Also, the proportion byweight of arsenic can be reduced to substantially 13% withoutdevitrification. As will be apparent from the area enclosed by solidline L the sulfur will range from about 25% to 78% by weight and thearsenic from about 13% to 56% by weight.

By maintaining at least about 4% telllurium in the composition, improvedtransmission properties are assured. As will be determined from thetriaxial diagram, the tellurium content will range from about 4% to 48%by weight.

' In producing the glass compositions provided by the invention, thefollowing procedure is employed:

A glass composition corresponding to about 40% S, 40% As, and 20% Te(designated as composition X in the table above) is prepared by weighingout a total of 500 grams of the elements of substantially high purity inthe comminuted or granulated form. The elements which are proportionedin accordance with the composition desired, are mixed and placed in aPyrex container provided with a Pyrex cover adapted to enable a stirringrod to pass through the cover into the container and to enable theprovision of an inert atmosphere of nitrogen, argon, etc.

The container is placed in a resistance wound vertical furnace andheated so that the temperature is raised to 200 C. as fast as possibleand held there so as to melt the sulfur. At this point the mass isstirred in order to maintain a uniform mixture between the liquid sulfurand the solid selenium and tellurium and to facilitate a smoothreaction. Upon completion of stirring, the mass is further heated at amaximum rate to 450 C. and the mixture stirred again. At this pointtellurium is molten. An exothermic reaction ensues an arsenic graduallyreacts with the sulfur. The temperature is then raised to 500 C. and themelt stirred again until all of the arsenic has reacted, the stirringbeing continued for about an hour at this temperature.

The molten bath which weighs about 500 grams is then cooled down toabout 450 C. at a rate of about 8 to 10 per hour while-stirring at adecreasing rate to prevent striae and the stirrer removed. The melt isthen cooled to 300C. over a fifteen hour period, this rate of coolingbeing important to prevent striae. At the end of this period, thecomposition is cooled from 300 C. to 200 C. in two and one half hours.

After the temperature has reached 200 C., the composition is subjectedto an annealing step comprising cooling it slowly to 155 C. over a 24hour period. The power of the furnace is turned off and the compositionfinally furnace cooled to room temperature.

The glass product obtained from the Pyrex container is about 4 incheslong and 2 inches in diameter. In subjecting the glass to a transmissiontest, a disc of about one quarter inch thick is first obtained from nearthe center of the cylindrical product by means of a diamond wheel. Theslice is ground to a thickness of about 2 mm. in an essentiallyconventional manner.

The resulting test sample is then mounted in a sample holder and putinto a sample beam of a Baird double beam recording infraredspectrophotometer (manufactured by the Baird Atomic Co. of Cambridge,Mass.). The instrument is operated to record the transmission ofinfrared radiation ranging from about 2 to 16 microns in wavelength. Theresults showed that this glass (40% As,

40% S and 20% Te) indicated a rather high cut-01f at a wavelength ofabout 13 microns at a transmission of 10%.

Another glass composition similarly produced comprising about 20% As,40% S and 40% Te (designated in the table as composition d). indicatedan even higher cut-off at a wavelength of about 13.3 microns for atransmission through the glass of 10%.

Still another glass comprising 55%. As, 40% S and 5%,

about 32% to sulfur and about 15% to 48% tellurium. It will be notedthat glass compositions X and d which gave fairly high cut-off valuefall within the foregoing preferred composition'range.

While the invention is concerned substantially with the ternarycompositions disclosed and claimed herein, it will be appreciated thatsmall amounts of other ingredients may betolerated in the ternarycomposition without adversely affecting substantially the transmissionproperties of the glass provided by theinvention.

It will be seen that I have described improved glass compositions andhave delineated a new fie'ld of glasses. My glasses have goodinfrared-transmitting properties and provide certain security in thevisual range by virtue of their substantial opacity to visible light.

While I have described the invention in detail with particular referenceto certain glasses, it will be understood that the invention is ofbroader scope and is defined in the claims which follow.

I claim: f

1. An optical, infrared-transmitting glass composition comprisingessentially a fused, vitreous,non-crysta.lline ternary mixture ofarsenic, sulfur andtellurium ispercentages by weight determined by thearea enclosed substantially within solid'line L of the accompanyingtriaxial diagram. I

2. An optical, infrared-transmitting glass composition comprisingessentially a fused, vitreous, non-crystalline ternary mixture ofarsenic, sulfur and tellurium in percentages by Weight ,of about 15'to52% arsenic, about 32% to 70% sulfur, and substantially the'balanceabout 15% to'48 tellurium.

References Cited in the file of this patent UNITED STATES PATENTS1,917,725 Lenander July 11, 1933

1. AN OPTICAL, INRARED-TRANSMITTING GLASS COMPOSITION COMPRISINGESSENTIALLY A FUSED, VITREOUS, NON-CRYSTALLINE TERNARY MIXTURE OFARSENIC, SULFUR AND TELLURIUM IS PERCENTAGES BY WEIGHT DETERMINED BY THEAEA ENCLOSED SUBSTANTIALLY WITHIN SOLID LINE L OF THE ACCOMPANYINGTRIAXIAL DIAGRAM.